Responsive carbon dot-embedded hybrid microgels for dual sensing of iron(iii) and ciprofloxacin†

A novel hybrid material was synthesized through the integration of nitrogen-doped carbon quantum dots (NCQDs) within a cationic poly(N-isopropylacrylamide-co-N-3-aminopropyl methacrylamide) (PNIPAM-co-APMH) microgel to create a highly sensitive, selective and multi-responsive system (NCQDs@PNIPAM-co-APMH) with an impressive quantum yield of 42%. The resultant hybrid microgel was shown to be an exceptional dual-functional sensor for detecting ferric ions (Fe³⁺) and ciprofloxacin (CIP). The detection of Fe³⁺ was marked by a “turn-off” fluorescence response, facilitated by dynamic quenching mechanisms. In contrast, upon the introduction of CIP into the Fe³⁺-quenched system (Fe³⁺-NCQDs@PNIPAM-co-APMH), a “turn-on” fluorescence response was observed, with a corresponding LOD of 0.41 μM. A logic gate framework was employed to achieve sequential sensing of Fe³⁺ and CIP in an “off–on” manner. Furthermore, the material exhibited excellent recovery rates, ranging from 86% to 108%, when applied to the analysis of real samples containing CIP. In addition to its sensing capabilities, the hybrid system was effectively utilized as a fluorescent ink, offering advanced anti-counterfeiting solutions and bolstering information security. This study highlights the substantial potential of NCQD-based hybrid materials in diverse sensing applications and their implications for practical innovations.